Las Vegas gunman Stephen Paddock fired from two windows of his 32nd-floor suite at the Mandalay Bay Sunday night, spraying gunfire for at least 10 minutes, authorities said.
Police said Paddock, 64, had 19 guns inside the suite, including several high-powered rifles.
"From the sound of the video, it's a fully automatic weapon," retired police officer Walter Philbrick said.
Philbrick is also a counter-terrorism instructor, private investigator, former gun shop owner and author.
Philbrick is currently writing a book called "Run, Hide or Fight," which is about how to survive an active shooter situation, and his research is frightening.
"Nowadays, the guy who kills tomorrow wants to beat the body count," Philbrick said. "If he killed 42, I want to kill 48."
"Does the American public need to have access to something like that? Does the American public need AR-15s?" Local 10 News reporter Jeff Weinsier asked.
"I don't think so," Philbrick said. "It's a rifle to kill people and it's a weapon of war."
Nevada is among the most gun-friendly states.
Big gun shows often gather there as a result and Nevada does not require a gun license or permit. Open carry is legal, assault weapons are legal and there is no magazine limit.
"Criminals are going to carry guns if there are laws or no laws," Philbrick said. "But the criminals aren't killing people in mass shootings. They're not that crazy. People have a psychological problem."